The invention relates to a sealing device for sealing non-circular, in particular polygonal, such as tetragonal, hexagonal, octagonal or elliptical, container orifices, wherein one or more induction loops are provided for sealing and the induction loops are adapted to the shape of the edge of the seal, and a process for sealing such container orifices, as well as a sealing washer used therein.
For economical stacking of receptacles they are preferably produced as non-circular tins, in particular tetragonal tins, for example for cocoa powder. Hereby more rectangular tins can be accommodated on the same floor space than with the provision of round tins. The latter are, however, preferred in production.
It is in fact found that the sealing of angular tins proves to be more difficult than the sealing of round tins. Therefore angular containers are frequently provided with round upper orifices. Tetragonal glass containers, the upper orifice edge of which can be glued down, prove to be particularly advantageous herein.
These glass containers are, however, not suitable for storing light-sensitive products, such as, for example, cocoa or espresso powder. If light were to enter the glass containers they would be decomposed or be subjected to other disadvantageous effects. It is therefore known to use a particular type of opaque plastics material containers especially for such products. Sticking foils on the upper encircling edge of these plastics material containers proves, however, to be problematic. For example, known foils do not stick sufficiently reliably or not at all on a HDPE (high density polyethylene) plastics material.
It is known to seal receptacles of this kind with light-sensitive products or even with milk or protein products by thermal conduction. Heat is here introduced directly into a suitable foil, whereby the plastics material surface of the container melts on to the orifice thereof. The heat can be produced in the foil by electric current or in another manner, for example by heat introduction. Products such as prawn salad, for example, are sealed in this manner with an aluminum foil or plastics material foil with a proportion of metal. Sealing by conduction, however, in most cases proves complicated and susceptible to faults. Moreover, it is unsuitable for the vagrious applications, for example with receptacles with light-sensitive products, such as cocoa and espresso powder or with HDPE containers with milk or protein products, as sealing through layers which insulate and seal the aluminum foil upwardly to the lid of the container is almost impossible.
It is further known to seal receptacles with a round filling orifice by induction sealing. A device is known from EP 0 223 517 B1 by means of which containers made of a plastics material with a lid cover also made of plastics material, as well as a metallic layer, are sealed by induction. The induction loop used in the device has a shaping corresponding to the edge to be sealed. It contains at least one corner shaping. A ferrite current concentrator unit is arranged herein. The induction loop engages with one surface into the cover for sealing. The ferrite current concentrator is arranged next to the induction loop.
The object of the invention is to provide a process and a device for induction sealing of non-circular, in particular polygonal, such as tetragonal, hexagonal, octagonal or elliptical, container orifices, which at little expense enables many sealing processes per unit of time, perfect sealing being guaranteed, particularly also in the corners.
This object is achieved for a sealing device for sealing non-circular, in particular polygonal, such as tetragonal, hexagonal, octagonal or elliptical, container orifices, wherein one or more induction loops are provided for sealing and the induction loops are adapted to the shape of the edge of the seal, in that the induction loops are dimensioned in such a way that a homogeneous field adapted to the measurements of the edge of the seal results in sealing, means are provided for controlling the induction loops with respect to the movement of the containers, parallel in time or speed, or means are provided for creating a balance of the production rate of the containers during sealing with respect to the induction loops and means are provided for timing the belts conveying the containers and the pressing and sealing process and for a possible adjustment of pressure during the sealing process.
The object is achieved for a process for sealing non-circular, in particular polygonal, such as tetragonal, hexagonal, octagonal or elliptical, container orifices in that, to ensure that the distance between the edge of the seal and the induction loop remains the same during the induction process, either the containers are halted to create a dwell time or induction loop and edge of seal are moved synchronously or at the same speed, the induction loops or plungers with induction loops are lowered from above on to lids of the containers with sealing washers to fit exactly, an induction sealing is carried out by applying a pre-determined pressure or without pressure, the induction loops or the piston(s) are conveyed upward after the induction sealing and the containers are guided onward out of the sealing device.
The object is achieved for a sealing washer used for the sealing, which is non-circular, in particular polygonal or elliptical, and has at least one metal foil and a layer made of a sealing material adapted to the material of the container on its underside pointing toward the container, in that a laminated upper part of the sealing washer arranged in the container lid is provided, and the metal foil, pointing toward the lid, is covered by a layer of paper or of thin foam foil or by a layer of wax, bonding emulsion or polyethylene and is connected to the upper part of the sealing washer.
The distance between the induction loop and the edge of the seal is preferably adjustable or discretionary, depending on shape, size and material of the edge of the seal and/or the sealing washer. For sealing by induction the induction loops are preferably bent in the same shape and dimension as corresponding to the upper surrounding edge of the seal of the container, either without pressure or under pressure. In the latter case the sealing washer is pressed against the edge of the seal either by the lid of the container or by a plunger.
Thus a device and a process for sealing non-circular container orifices are created, in which the induction takes place evenly. Combustion of the longitudinal faces of angular or elliptical container orifices or leaving corners open is thus avoided. By means of the possible pressure-less sealing or sealing which can be provided using available pressure when screwing on or attaching the lid to the neck of the container, additional expense for a pressure device, which is otherwise useful and customary for ensuring perfect sealing, is advantageously saved. Even lengthening of the time for the sealing process does not occur, as either induction loop and container lid are moved in parallel synchronously or at the same speed or the time loss occurring because of the halting of the containers for sealing is counterbalanced by parallel motion of several containers during the sealing process. In the actual process of filling the containers parallel motion of this kind is already customary in the food industry.
By providing dual coils or simply coils running dually on the induction loops, non-homogeneities no longer occur in the region of the inlets and outlets for the current from a loop. An exactly matched homogeneous field results. Sealing of the non-circular containers is thus guaranteed in an optimal manner, in particular also at the corners.
The induction loops are preferably provided in the plunger(s). They can, however, also be provided next to the plungers or exclusively, in other words without additional plungers. Preferably a large plunger is provided in the sealing device with induction loops provided next to one another, corresponding to the distances of containers preferably in parallel motion during the induction process. For this embodiment, however, several plungers arranged next to one another or behind one another can also be arranged with correspondingly dimensioned induction loops. The induction loops are preferably arranged behind one another when they are moved on a conveyor belt together with the containers synchronously and/or at the same speed as the containers.
The edges of the seals of the containers are preferably already provided respectively with a correspondingly dimensioned sealing washer and a lid. It is possible, however, for them not to be provided with lid and sealing washer until they are in or in the region of the sealing device.
For sealing with a plunger the plungers are lowered with the induction loops at a certain pressure on to the containers. The plunger preferably presses a metal foil provided in the sealing washer through the lid as a so-called antenna or means for producing the induction sealing in connection with a sealing layer on to the upper surrounding edge of the container. If current is charged into the induction loops the metal foil sticks to the upper surrounding edge of the seal of the container. The connection of metal foil and surrounding edge of seal is the same at every point of the upper surrounding edge of the container. Optimum sealing with the foil takes place even at the corners of the container orifice, as the field created by the induction loop is adapted exactly to the measurements of the upper surrounding edge of the seal of the container and is homogeneous.
To create complete homogeneity of the field a dual coil of the induction loop is preferably provided.
The distance between the induction loop and the edge of the seal can preferably also be selected depending on shape, size and material of the edge of the seal and/or the sealing washer.
Adaptation to different measurements and shapings of container orifices occurs by providing an assortment of various induction loops, in particular integrated into plungers, with corresponding measurements and shapes. If the container edge shapes and measurements are altered the induction loops or induction loops with plunger are completely changed. After the sealing process the induction loop or the plunger(s) is/are conveyed upward away from the containers. A driving device transports the containers out of the sealing device, in particular after previously being in parallel motion to create a dwell time and to balance the production rate, back into a row.
It is particularly preferable that means are provided for the induction loops for setting a pre-determinable current to create an adapted, homogeneous field, and for the plungers means for setting a pre-determinable pressure effective during the induction process. Preferably control devices are provided for timing the conveyor belts, the pressing and sealing process and for possible pressure adjustment during the sealing process. Preferably a thermoplastic material, in particular polymers, such as polypropylene, polyester, PVC or such, can be provided as the material for the container, or particularly preferred HDPE (high density polyethylene) or even glass.
The sealing washers have, additionally to the metal foil, in particular aluminum foil, and the sealing layer, which is arranged pointing toward the product in the container, a layer of paper, thin foam foil or of wax, bonding emulsion or polyethylene facing the lid of the container, in other words under the upper part of the sealing washer inserted therein. The latter is preferably made of polyethylene or polypropylene foam, laminated, or of laminated cardboard.